Method and arrangement for touchless detection of data of uneven surfaces

ABSTRACT

A method for detecting data of an uneven surface of an object includes the following steps: illuminating at least one of stripes and a grid on the uneven surface using at least one light source; detecting, without a touching contact, light reflected from the uneven surface at a plurality of discrete locations so as to create a partial image of the uneven surface at each of the plurality of discrete locations; selectively analyzing each of the partial images; and combining at least portions of the partial images into an overall image of the uneven surface.

The present invention relates to a method and an arrangement fordetection of data of uneven surfaces, in particular for acquisition ofbiometric data at faces and fingers, using a light source forillumination of the uneven surface, an imaging optical system and ananalyzing facility for electronic image processing.

BACKGROUND

The acquisition of biometric data is required for many applications. Inparticular, for the identification of persons and for control ofauthorization, the accurate and as forgery-proof as possible acquisitionof this data is required. Because of their manifold advantages,touchless methods are often used thereby.

On this, a set of possibilities is described in the prior art.

According to European Patent Document EP 0 194 783 B1, a device fordetection of data of uneven surfaces is known, where a transparent plateexhibits two opposing surfaces, wherein an uneven surface havingrecesses and protrusions, which is to be detected, is pressed againstone of the even surfaces, comprising a light source for illumination ofthe uneven surface at the contact section through the transparent plateand an optical element for guidance of the light, which is scattered bythe uneven surface, to the light detector.

The light source is arranged in such a way that it illuminates thecontact section at an illumination angle which is smaller than acritical angle, in order to that the light incident from the source ontothe contact section is not totally reflected, whereby a part of thelight, which is scattered at the protrusions of the uneven surface, isundergoing an inner total reflection at least at the second surface ofthe plate, in order to propagate in a direction against the opticalelement, whereas the light which is scattered at the recesses isundergoing none such inner total reflection, whereby the two kinds ofscattered light are separated spatially, wherein the optical element isarranged to guide only light scattered at the protrusions to thedetector.

Furthermore, in European Patent Document EP 0 359 554 B1, an arrangementfor the determination of fingerprints is described, with which zones ofthe finger are imaged to a light receiver. The arrangement possesses alight source, means for guiding the light rays which are running fromthe light source onto the surface of the finger to be detected, anoptical imaging system which creates an image of an irradiated part ofthe sample, a light detector facility for detecting the image and afacility for the output of a detection signal. Using the arrangement, itshall be determined if the sample is a biological object or animitation. Therefore, the light detector is provided with a lightreceiver area which is divided into zones so that an image of theirradiated part is created on the light receiver area. The lightdetector possesses separate optical outputs for the plurality of lightrays received respectively. The discrimination if it is the matter of anauthentic object, i.e. a vital finger, or an imitation is carried out byanalyzing the course of the light, wherein the phenomenon that, in caseof an authentic finger, the light partly enters the finger and, in caseof an imitation, does not enter into it so that different courses oflight result, is exploited.

In addition, according to European Patent Document EP 1 073 988 B1, asystem for recognition of hand and finger lines is known, which servesfor the identification of persons. Using this system, hand and/or fingerlines, patterns of dermal ridges, patterns of the subcutis or the likeare acquired optically for acquisition of an image by using a lightsource, a polarization filter and a camera without mechanical movementsof the arrangement. The optical acquisition is carried out by means ofpolarization filters placed in the optical path of illumination and inthe optical path of imaging and by means of a fixedly arranged camera.

In the case of the known arrangements, it is disadvantageous that thecontrast for the imaging of the structures is low so that a secureanalysis of the images is made very difficult.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and anapparatus of the initially said type which enable touchiessly scanningof uneven surfaces, in particular of a relief made up of dermal ridges,and creating an image of the surfaces true to original with highcontrast.

The present invention provides a method for recognition of biometricdata, in particular for the recognition of characteristics of fingersand of faces of persons, comprising: illuminating at least one ofstripes and a grid on the uneven surface using at least one lightsource; detecting, without a touching contact, light reflected from theuneven surface at a plurality of discrete locations so as to create apartial image of the uneven surface at each of the plurality of discretelocations; selectively analyzing each of the partial images; andcombining at least portions of the partial images into an overall imageof the uneven surface. The present invention also provides anarrangement for a touchless detection of data of an uneven surface of anobject, comprising: an imaging optical system including an electroniccamera oriented perpendicular to the uneven surface; a plurality ofline-shaped light sources for illuminating the uneven surface disposedin row on each side of the electronic camera; an analyzing unit forelectronic image processing including an electronic control unit coupleto the electronic camera and configured to assign a partial imagecorresponding to each of the plurality of light sources and to processthe partial images into an overall image.

Advantageous embodiments are described in the specification and in theclaims.

The present invention preferably serves for the optical scanning ofdermal ridges. The dermal ridges are embossed and make up acharacteristic relief. They distinguish themselves by a higher glossthan the adjacent spacings. By the glossy surface, the light isreflected directionally to a large fraction, wherein the coloration ofthe reflected light is small. In contrast, the spacings reflectdiffusely with a red coloration.

As glossy surfaces reflect directionally, i.e. the light is reverberatedaccording to the law of reflection, this means that light sources mirrorthemselves in the reflecting area. The dermal ridges thus mirror thelight coming from the light source. To achieve a true-to-original andhigh-contrast image of the ridges, it has to be ensured that only a topedge of the ridge is imaged. As the slope of the finger ridges varies upto about 50° along the finger, for the illumination of the outer ridgeswhich are sloped to a higher extent, the light source is placeddifferently than the light source intended for the illumination of theobject's center.

Conveniently, the camera is arranged perpendicularly to the object sothat the light source serving for illumination should be arrangeddirectly next to the camera. However, the camera placed in such a waydoes not illuminate the outer ridges at their top edges anymore, butrather laterally of those edges. This causes an apparent deformation ofthe ridges in the image. In order to illuminate the border areas of theobject, the light sources are therefore arranged farther outwards.

An advantageous embodiment of the present invention uses the light'scolor with which the object is illuminated in order to increase thecontrast of the image.

If the object is illuminated directionally using white light, the fingerridges appear glossy white, but the spacings diffusely red. By colorfiltering during the imaging and/or by colored illumination, thecontrast can be raised.

In the method according to the present invention, an object to bedetected is illuminated in such a way that, in each area of the object,the top edge of the dermal ridges reflects.

In order to identify a finger, the illumination is carried out in such away that the surface normal in each area of the finger makes up thebisecting line of the angle between the illumination and the camera'sobjective with the finger's axis as the angular point. But the lightsource shall not be extensive thereby, but shall not exceed an extent of15 mm transverse to the finger's axis.

The method can be realized using different arrangements. In particular,such arrangements are suitable which perform the following functions:

-   -   moving the illumination on a path arranged around the object,    -   moving the camera on a path arranged around the object,    -   arranging several cameras around the object,    -   arranging several switchable illuminations,    -   arranging several differently colored illuminations and several        color-selective cameras,    -   arranging several differently colored illuminations and one        color camera in an arrangement, wherein the above condition of        angle is satisfied.

The spacings between the single dermal ridges are not glossy indeed, butalso not dark. In the image, they appear colored red. However, in redlight, the structure of the object is hardly recognizable. The contrastof the image can be further increased by creating an image congruent tothe images of the dermal ridges in the red or infrared spectral rangerespectively and subtracting this image from the structure image as auniform darkness value.

Using the arrangement according to the present invention, a preferablylarge part of the object is illuminated by the given arrangement in sucha way that the light source mirrors itself always exactly in the topedge of the dermal ridge. Only in this case, a true-to-original imageresults.

If the illumination was carried out using a sufficiently large lightsource it would indeed be ensured everywhere that the top edge of theridges mirror any part of the light source. But the side surfaces shine,too, as the remaining parts of the light source responsible for otherareas illuminate them. In this case, the dermal ridges appear broad, thecontrast between them can get lost completely and the borders of theridges are imaged in a deformed manner.

It is possible to design the light source in a way such that only lightrays are emitted which meet in an axis of the object. This can beachieved, for example, by using parallel light which is focussed bymeans of a cylindrical lens. Admittedly, this requires a certain effort.Furthermore, the object needs to be placed exactly centrically.

In order to prevent disturbing light from falling onto the sidesurfaces, the light source can be moved or the light sources areswitched on one after the other. Then, for each situation, a separateimage is taken.

An advantageous embodiment is designed to arrange several cameras ofwhose single images an overall image is composed which uses only theaccurately illuminated image parts. The difficulty occurring thereby,that the boundaries do not fit exactly because of the unavoidabledifferences of the single perspectives, can be solved using anappropriate software.

Therefore, it is advantageous to create a separate image using only onecamera for each light source and to concatenate the respective accurateareas of the single images to an overall image. Thereby, a largefraction of the images is not required.

This is achieved, for example, by using a CMOS camera, from which eacharbitrary pixel can be read out selectively separately. Then, for eachlighting situation, one can sequentially read out the well illuminatedarea of the matrix, as it is known where this area must lie for eachlight source. Therewith, creating the image is much faster than creatingan overall image by joining together. Practically, this can be as fastas if one overall image is taken. During the imaging, the illuminationis just switched synchronously through the lighting situations.

Another embodiment uses colored light sources so that the separation iscarried out via the single color excerpts. So here, after taking theimage, from each color excerpt the optimally illuminated area is takenout and an overall image is created in a frame buffer as black and whiteimage. It is advantageous here that the procedure is performedsimultaneously. The effort in software and the lower resolution of thecolor camera have to be regarded to be disadvantageous.

An especially advantageous embodiment for the recognition of fingers isconstituted by an arrangement, wherein a successive switching of thelighting situation is carried out and a CMOS camera is read outsynchronously and selectively. Advantageously, the camera is arranged orthe reading out is designed, respectively, in such a way that areasparallel to the finger's axis are always read out simultaneously.Purposefully, the light source is also arranged longitudinallyparallelly thereto. Thus, the finger is scanned synchronously andselectively line by line, wherein the lines are aligned parallelly tothe finger's axis.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention is further explained consideringan example of an embodiment. The example concerns the recognition of thestructure of a finger's dermal ridges.

In the appropriate figure, it is shown by:

FIG. 1: a schematic illustration of an arrangement with a camera andseveral light sources arranged around the finger;

FIG. 2: an arrangement with additionally attached reference diodesshining red; and

FIG. 3: an embodiment with several cameras.

DETAILED DESCRIPTION

In case of the arrangement depicted in FIG. 1, the finger 1 to bescanned is illuminated using a light source consisting of eight LED rows3 and imaged using a centrally arranged camera 2.

The LED rows 3.1 to 3.4 and 3.1′ to 3.4′ are arranged in anapproximately circular path around the finger 1, wherein adjacent LEDrows always exhibit different colors, respectively. The colors repeatafter a distance in which no mutual interaction takes place. In thepresent embodiment, LED rows of four different colors 3.1 to 3.4 and3.1′ to 3.4′ respectively, are used. The camera 2 is provided with afacility which creates a separate image for each color.

It is also possible that the light sources are arranged in an array oflight emitting diodes.

In FIG. 2, an advantageous embodiment is depicted, where, between theLED rows 3.1 to 3.4 and 3.1′ to 3.4′ respectively, an additional LED row3.R which emits red light is arranged between adjacent rowsrespectively. Therewith, in the camera 2, a fifth color excerpt imagecan be created which exhibits a weak structure only and serves as areference of brightness for calculationally joining together the singlecolor excerpts to an overall image. Using the camera 1, for each lightsource a separate image is created and the single images areconcatenated to an overall image. This joining together is carried outusing an electronic imaging unit not depicted here.

Preferably, for camera 1 a CMOS camera is used at which the pixels canbe read out selectively and can be processed further. For each LED row3, the matrix area which is assigned to the appropriate edge is read outsuccessively. During the imaging, the lighting situations aresynchronously switched through.

FIG. 3 shows an embodiment in which several cameras 2 are used. In thisvariant, an overall image is composed of the single images gained by allcameras 2, by means of the electronic imaging unit, wherein the overallimage uses the accurately illuminated image parts only.

Thereby, illumination and/or receivers can be merged by means of beamsplitters.

1. A method for detecting data of an uneven surface of an object, themethod comprising: illuminating at least one of stripes and a grid onthe uneven surface using at least one light source; detecting, without atouching contact, light reflected from the uneven surface at a pluralityof discrete locations so as to create a partial image of the unevensurface at each of the plurality of discrete locations; selectivelyanalyzing each of the partial images; and combining at least portions ofthe partial images into an overall image of the uneven surface, whereinthe illuminating includes moving the at least one light source on a patharound the object, and wherein the detecting at the plurality ofdiscrete locations is performed at different points in time.
 2. Themethod as recited in claim 1, wherein the object includes at least oneof a face and a finger, and wherein the data includes biometric data. 3.A method for detecting data of an uneven surface of an object, themethod comprising: illuminating at least one of stripes and a grid onthe uneven surface using at least one light source; detecting, without atouching contact, light reflected from the uneven surface at a pluralityof discrete locations so as to create a partial image of the unevensurface at each of the plurality of discrete locations; selectivelyanalyzing each of the partial images; and combining at least portions ofthe partial images into an overall image of the uneven surface, whereinthe at least one light source includes a plurality of light sourcesdisposed around the object in an arc-shaped configuration, wherein theilluminating includes sequentially switching on each of the plurality oflight sources, and wherein the detecting is performed sequentiallyaccording to the switching.
 4. The method as recited in claim 1, whereinthe detecting is performed using a plurality of cameras and thecombining into an overall image includes combining only selectedilluminated areas of each of the plurality of partial images.
 5. Themethod as recited in claim 3, wherein only one camera is used to createeach of the partial images corresponding to each light source, andwherein respective selected areas of each of the partial images arecombined into the overall image.
 6. A method for detecting data of anuneven surface of an object, the method comprising: illuminating atleast one of stripes and a grid on the uneven surface using at least onelight source; detecting, without a touching contact, light reflectedfrom the uneven surface at a plurality of discrete locations so as tocreate a partial image of the uneven surface at each of the plurality ofdiscrete locations; selectively analyzing each of the partial images;and combining at least portions of the partial images into an overallsimage of the uneven surface, wherein the selectively analyzing isperformed using different wavelengths, wherein the illuminating includesdirectionally illuminating with white light, wherein the detecting isperformed by a camera, wherein color filtering single areas is performedduring the detecting so as to create partial images of differentwavelengths, wherein the analyzing includes selecting an area andassigning a desired location to the area, and wherein the combiningincludes combining at least portions of the partial image into anoverall black and white image in a frame buffer.
 7. The method asrecited in claim 6, wherein the illuminating is performed using light ofdifferent wavelengths.
 8. A method for detecting data of an unevensurface of an object, the method comprising: illuminating at least oneof stripes and a grid on the uneven surface using at least one lightsource; detecting, without a touching contact, light reflected from theuneven surface at a plurality of discrete locations so as to create apartial image of the uneven surface at each of the plurality of discretelocations; selectively analyzing each of the partial images; andcombining at least portions of the partial images into an overall imageof the uneven surface, wherein the selectively analyzing is performedusing different wavelengths wherein the at least one light sourceincludes a plurality of light sources synchronously switched on duringthe detecting, and wherein the detecting includes only one camera so asto create each of the partial images for each light source, and furthercomprising selecting an area for each of the partial images for eachlighting situation using an electronic control unit.
 9. A method fordetecting data of an uneven surface of an object, the method comprising:illuminating at least one of stripes and a grid on the uneven surfaceusing at least one light source; detecting, without a touching contact,light reflected from the uneven surface at a plurality of discretelocations so as to create a partial image of the uneven surface at eachof the plurality of discrete locations; selectively analyzing each ofthe partial images; and combining at least portions of the partialimages into an overall image of the uneven surface, wherein the objectincludes a finger, and wherein the detecting includes scanning thefinger line by line selectively, wherein the lines are aligned parallelto an axis of the finger.
 10. An arrangement for a touchless detectionof data of an uneven surface of an object, comprising: an imagingoptical system including an electronic camera oriented perpendicular tothe uneven surface; a plurality of line-shaped light sources forilluminating the uneven surface disposed in row on each side of theelectronic camera; an analyzing unit for electronic image processingincluding an electronic control unit coupled to the electronic cameraand configured to assign a partial image corresponding to each of theplurality of light sources and to process the partial images into anoverall image.
 11. The arrangement as recited in claim 10, wherein theobject includes a finger and wherein the data includes biometric data.12. The arrangement as recited in claim 10, wherein the plurality ofline-shaped light sources includes light emitting diodes.
 13. Thearrangement as recited in claim 10, wherein the electronic camera isconfigured to create each of the partial images for each light source,wherein the plurality of light sources are configured to be sequentiallyswitched on, wherein the analyzing unit is configured to process onlyselected areas of each of the partial images, and wherein the electroniccontrol unit is configured to read out an area of a matrix for eachlighting situation and to assign the area of the matrix to a desiredlocation on the object.
 14. The arrangement as recited in claim 10,wherein the electronic camera is a CMOS camera.
 15. The arrangement asrecited in claim 10, further comprising a plurality of additionalcameras disposed side by side in a row.
 16. The arrangement as recitedin claim 10, wherein the plurality of light sources includes a whitelight source oriented perpendicular to a center of the uneven surface,and further comprising a plurality of additional cameras configured totake spectrally filtered partial images disposed in a row alongside thewhite light source.
 17. The arrangement as recited in claim 10, whereinthe plurality of light sources include at least two light sourcesradiating at a same wavelength and a third light source disposed betweenthe at least two light sources and radiating at a different wavelength.18. The arrangement as recited in claim 12, wherein the light emittingdiodes radiate at wavelengths in a range of about 400 nm to about 3 μm.19. The arrangement as recited in claim 12, further comprising anadditional light source radiating red and disposed in the row as anillumination of reference.
 20. The arrangement as recited in claim 19,wherein the additional light source radiates at a wavelength of at leastone of 660 nm and 800 nm.